[PATCH v2 0/4] STM32 DMA-MDMA chaining feature

[Amelie Delaunay <amelie.delaunay@foss.st.com>]

This patchset (re)introduces STM32 DMA-MDMA chaining feature.

As the DMA is not able to generate convenient burst transfer on the DDR,
it penalises the AXI bus when accessing the DDR. While it accesses
optimally the SRAM. The DMA-MDMA chaining then consists in having an SRAM
buffer between DMA and MDMA, so the DMA deals with peripheral and SRAM,
and the MDMA with SRAM and DDR.

The feature relies on the fact that DMA channel Transfer Complete signal
can trigger a MDMA channel transfer and MDMA can clear the DMA request by
writing to DMA Interrupt Clear register.

A deeper introduction can be found in patch 1.

Previous implementation [1] has been dropped as nacked.
Unlike this previous implementation (where all the stuff was embedded in
stm32-dma driver), the user (in peripheral drivers using dma) has now to
configure the MDMA channel.

[1] https://lore.kernel.org/lkml/1538139715-24406-1-git-send-email-pierre-yves.mordret@st.com/

Changes in v2:
- wrap to 80-column limit for documentation
- add an entry for this documentation in index.rst
- use simple table instead of csv-table in documentation

Amelie Delaunay (4):
  docs: arm: stm32: introduce STM32 DMA-MDMA chaining feature
  dmaengine: stm32-dmamux: set dmamux channel id in dma features
    bitfield
  dmaengine: stm32-dma: add support to trigger STM32 MDMA
  dmaengine: stm32-mdma: add support to be triggered by STM32 DMA

 Documentation/arm/index.rst                   |   1 +
 .../arm/stm32/stm32-dma-mdma-chaining.rst     | 415 ++++++++++++++++++
 drivers/dma/stm32-dma.c                       |  56 ++-
 drivers/dma/stm32-dmamux.c                    |   2 +-
 drivers/dma/stm32-mdma.c                      |  70 ++-
 5 files changed, 541 insertions(+), 3 deletions(-)
 create mode 100644 Documentation/arm/stm32/stm32-dma-mdma-chaining.rst

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2.25.1